A fuel cell is an electrochemical cell comprising two electrodes separated by an electrolyte. The fuel in the electrochemical cell oxidized to produce electricity on demand. The fuel is depleted during operation and must be replenished. Hydrogen, methanol, and ethanol, are examples of fuel that have been used in fuel cells. A fuel is supplied to the anode and an oxidant, e.g. oxygen or air, is supplied to the cathode. Electrochemical reactions occur at the electrodes, and the chemical energy of the fuel and the oxidant is converted to electrical energy and heat. Electrocatalysts are used to promote the electrochemical oxidation of the fuel at the anode and the electrochemical reduction of oxygen at the cathode.
Dimethyl ether (DME) is a clean-burning alternative to diesel fuel that meets strict emissions standards in combustion engines. DME is derived from natural gas but can also be synthesized from biomass on-site. As such, DME is a sustainable and highly distributed energy source. DME has properties similar to propane and can utilize established fueling infrastructure and handling procedures. In addition to its use in internal combustion engines, the convenience of DME generation and transport can be exploited to overcome the high-pressure requirements of hydrogen fuel in more efficient electrochemical fuel cells. Fuel cell-driven vehicle efficiencies are among the highest of all vehicle technologies. The electrochemical process with half-cell potentials is as follows:(CH3)2O+3H2O=2CO2+12H++12e−  Anode:3O2+12H++12e−=6H2O  Cathode:(CH3)2O+3O2=3H2O+2CO2.  Overall:
Relative to other non-hydrogen fuels envisioned for use in electrochemical cells, DME has many advantages. DME is a nontoxic substance and is more energy-dense than hydrogen. DME has a lower dipole moment than methanol which limits fuel crossover from anode to cathode. Additionally, DME is the simplest ether, and can be more efficiently oxidized than ethanol through electrocatalytic C—O bond cleavage. Unlike ethanol, DME does not interfere with world food production.
However, a key obstacle to the commercial realization of DME fuel cells is the identification of a suitable electrocatalyst. Despite previous investigations on the use of DME in operating fuel cells, few studies provide fundamental electrochemical characterization of highly dispersed electrocatalysts required in practical fuel cell design. In one such study, the most active electrocatalyst for DME oxidation at low current densities was found to be highly dispersed commercial PtRu alloy nanoparticles supported on carbon (PtRu/C). The potential observed at a slow scan cyclic voltammetry (CV) oxidation current of 0.05 A/gPt was 0.30 V versus RHE, or 0.15 V below that of commercial Pt on carbon in IM DME-saturated H2SO4 solution. Chronoamperometry yielded a stable mass activity of greater than 1 A/gPt at 0.40 V vs RHE, or more than an order of magnitude higher than that of commercial Pt/C catalyst under the same solution conditions. This increase is ascribed to the incomplete oxidation of DME to CO at low potentials in the case of pure Pt, as well as to the ability of alloyed Ru to activate H2O adsorption and promote CO conversion to CO2. However, at higher potentials (e.g., approaching a peak potential at 0.8 V), the activity of Pt/C was found to be much greater than that of PtRu/C, presumably due to reduced Pt surface area in the alloy. This finding was confirmed in operating DME fuel cells, where electrocatalysts with increasing Ru concentration relative to Pt exhibit lower potential at reaction kinetic-limited currents.
Consequently, there is a continuing need in the art for more efficient fuel cell catalysts than commercially available PtRu—C or Pt/C. Such new catalyst would enable the utilization of DME as a bridge-fuel until hydrogen infrastructure becomes sufficiently widespread. Thus, there is a need thus for: (i) synthesis of new materials with more efficient and higher catalytic activity; (ii) new methods for synthesis of these new materials and their precursor materials; and (iii) fuel cells employing these new materials.